People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

REM Sleep Disorder May Cause Alzheimer’s And Other Brain Diseases

Researchers have discovered that REM (rapid eye movement) sleep behavior disorder, which causes people to act out their dreams, is a predictor of brain diseases such as Parkinson's and Alzheimer's. Photo courtesy of Shutterstock.

Dreaming may be the single most beautiful state of consciousness available to us on earth; our minds take flight while our bodies remain at rest. Unfortunately, those who suffer from sleep disorders may be cheated of one of life’s finest experiences while also wreaking havoc on their health. Now, researchers at the University of Toronto have discovered that a particular sleep disorder that causes people to act out their dreams is a predictor of brain diseases such as Parkinson's and Alzheimer's. "Rapid-eye-movement sleep behaviour disorder (RBD) is not just a precursor but also a critical warning sign of neurodegeneration that can lead to brain disease," said Dr. John Peever, associate professor and lead author of the newly published study. “In fact, as many as 80 to 90 per cent of people with RBD will develop a brain disease."

What is sleep?

Sleep is a phenomenon that involves moving through three gates of consciousness: wakefulness, rapid eye movement (REM) sleep, and non-rapid eye movement (N-REM) sleep. Commonly, we dream during REM sleep. Surprisingly, the electrical activity of our brains during REM (recorded by an electroencephalogram) looks similar to the activity during wakefulness with our neurons functioning much the same. A powerful difference, though, is that REM sleep is characterized by a temporary muscle paralysis. This is the reason why we may dream of leaping through the air, yet we remain safe and relatively still in your bed.

However, for some people with sleep disorders, the neurological gates between different states of consciousness don’t open and close fluidly. REM sleep behavior disorder (RBD), for instance, is a rare neurological condition in which the temporary muscle paralysis that normally occurs during REM sleep simply doesn’t happen. This causes a person with RBD to talk, twitch, jerk, or even fully enact the action taking place in their dreams. This may seem harmless, but too often sufferers of this disorder cause injury to themselves as well as to their bed partners.

To fully explore RBD, a team of researchers led by Peever investigated previous scientific studies of the disorder and the neuroscience underpinning it. What they discovered was that in 80 percent of all cases of RBD, development of synucleinopathies occurs. The term synucleinopathies encompasses a group of neurodegenerative disorders that includes Parkinson's disease, dementia with Lewy bodies, and and multiple system atrophy. “This link suggests that neurodegenerative processes initially target the circuits controlling REM sleep,” wrote the authors in their published research.

Delving deeper into the underlying neuroscience, the team also discovered evidence that RBD results from a breakdown of the neural network underlying REM sleep paralysis. In other words, the research suggests neuro-degeneration might first occur in areas of the brain that control sleep before attacking regions that cause more common diseases, such as Alzheimer's. "It's important for clinicians to recognize RBD as a potential indication of brain disease in order to diagnose patients at an earlier stage," said Peever in a press release. He and his team believe drugs reducing degeneration of brain circuits might be used in RBD patients to prevent (and protect) them from developing more severe degenerative disorders as they age. Possibly, too, their research might widen our understanding of Alzheimer's and lead to treatments for that disease as well.